Two balls of mass 0.4 kg and 0.8 kg are connected by a low-mass spring. This device is thrown through the air with low speed, so air resistance is negligible. The motion is complicated: the balls whirl around each other, and at the same time the system vibrates, with continually changing stretch of the spring. At a particular instant, the 0.4 kg ball has a velocity <8, -5, 8> m/s and the 0.8 kg ball has a velocity <3, 2, 4> m/s. (a) At this instant, what is the total momentum of the device?

(b) What is the net gravitational (vector) force exerted by the Earth on the device?

(c) At a time 0.10 seconds later, what is the total momentum of the device?